1. Field of the Invention
The present invention relates generally to coding schemes for digital transmission systems. More particularly, the present invention relates to systems and methods for protecting digital video content during transmission.
2. Description of Background Art
Secure, high-speed communication of information among different devices is increasingly important as electronic and computer technology continues to evolve. For example, it is now more desirable than ever to provide for high-speed communications among different chips on a circuit board, different circuit boards in a system, and different systems with each other. There is a need to provide such communications at high speeds in view of the increasing amount of data required for data communications in intensive data consuming systems using graphical or video information, multiple input-output channels, local area networks, and the like.
There is also a need for secure communication as a result of the increased value of the communicated content and the increased likelihood that communicated content will be copied or altered. Communicated content is increasing in value as a result of an increase in the amount of communicated content and an increase in the quality of communicated content. For example, popular movies continue to become widely available on DVD format. Such valuable content provides a large incentive for potential digital video pirates. In addition, since digital information replicates perfectly, copying a digital source is easier than copying an analog source.
Thus, it is particularly desirable to enable individual personal computers, workstations, or other computing devices, within which data is normally internally transferred using parallel data buses, to communicate with each other over relatively simple transmission lines in a manner that discourages digital content pirating. Such transmission lines typically include only one or two conductors, in contrast with the 64-bit and wider data paths. In the case of video data transmission to computer displays, as well as in the case of high-speed video input from digital cameras to computer systems, existing interconnection interfaces typically employ parallel data paths. The requisite bandwidth of such interconnection systems has increased as a consequence of increased display resolution.
Various techniques exist for improving the characteristics of transmission over serial links. For example, transmission codes may be employed to alter the frequency spectrum of the transmitted serial data so as to facilitate clock recovery and enable AC coupling. Each transmission code will also typically provide special characters, not included within the data alphabet, to be used in character synchronization, frame delimiting, as well as perhaps for diagnostic purposes.
Coding may also be employed to reduce transmission bandwidth as a means of limiting the signal distortion occurring during propagation through the transmission medium. In the case of wire links, it is desirable to utilize codes with no DC and little low frequency content in order to allow for DC isolation of the driver and receiver circuitry from the transmission line, as well as to reduce signal distortion on the line. An efficient coding system should also be disposed to encode clock information with the encoded data in a manner allowing for extraction of the clock information during decoding. This obviates the need for provision of a separate clock signal over a dedicated clock line, since the clock information recovered during decoding may be instead used by the receiver circuitry. Thus, there is a need for an encryption scheme that preserves desirable properties of a serial link transmission code and yet, at the same time, is difficult to decipher. The encryption scheme should make it particularly difficult for pirates to tap the transmission line in an effort to record the raw digital stream into a digital storage media.